The present invention relates to a method of operating a dry quenching apparatus for hot coke, and particularly to a method of operating the apparatus under optimal conditions for maximum benefits.
In a conventional coke oven, hot coke which has been pushed out of the oven is quenched with a water spray. This quenching process is referred to as wet quenching. Wet quenching has the disadvantages that a very large amount of heat of the hot coke is wasted by release into the air and that steam which is produced during water-quenching is accompanied by dust, which is dispersed into the environment.
Therefore, dry quenching apparatuses (hereunder also referred to as "coke dry quenchers(CDQ)") have recently been employed. A dry quenching apparatus can not only recover sensible heat of hot coke but can also prevent the spread of dust. In addition, it can increase the strength and lower the water content of the coke.
Furthermore, a dry quenching apparatus has the advantage that combustible gases such as methane, hydrogen, and carbon monoxide which are contained in the hot coke and monoxide gas which is produced by combustion of coke can be recovered.
However, it has also the disadvantage that during dry quenching, powdering and combustion of the coke are inevitable, resulting in a decrease in the yield of coke.
A conventional dry quenching apparatus for hot coke has a capacity of 30-50 tons/hour. A plurality of dry quenching apparatuses must be provided for one coke oven battery. Recently a large-scale dry quenching apparatus with a capacity of 100-200 tons/hour has been employed since it is economical to construct and easy to operate. A single dry quenching apparatus of this size can treat the output of an entire battery of coke ovens.
An arrangement of coke oven batteries and coke dry quenchers (CDQ) of this type in which each coke oven battery is associated with one quenching apparatus having a large capacity is shown in FIG. 1. Hot coke from battery A is supplied to CDQ No. 2 and that from battery B is supplied to CDQ No. 1.
FIG. 2 is a schematic partially sectional view of a dry quenching apparatus for hot coke. Hot coke discharged from a coke oven is loaded into a coke bucket 1 disposed on a bucket car and then lifted by a winch 2 to the top of a quenching tower 3, i.e., a CDQ. The hot coke is then charged into a prechamber 4 through the bucket 1' lifted to the top of the quenching tower 3.
After being charged into the prechamber 4, the hot coke descends within a cooling chamber 5 while being cooled by contact with an inert gas such as nitrogen gas which is blown into the cooling chamber 5 through a blast head 7 by a gas circulating fan 6. After it is cooled, the coke is discharged from the quenching tower 3 by means of a discharge device 8. A circulating gas which is heated by contact with the hot coke is subjected to dusting in a waste gas flue 9 and then is passed into a heat exchanger 10. After passing through the heat exchanger 10, the cooled gas is subjected to dusting with a plurality of cyclone separators 11 and is blown into the cooling chamber 5 with the fan 6 for re-use as a cooling gas. High-temperature, high-pressure steam which is recovered from the heat exchanger 10 is supplied to an apparatus employing steam, such as a turbo-generator (not shown).
In a quenching apparatus of this type, the discharge rate of cooled coke is determined so as to maintain a given level of hot coke within the prechamber 4.
Since discharging of hot coke from the coke oven is carried out intermittently, hot coke from the oven is charged into the prechamber 4 at intervals of 7-9 minutes. However, hot coke is not charged into the prechamber 4 at all during the period that the coke oven is running (1-2 hours).
Thus, the delivery rate of cooled coke through the discharge device 8 is controlled so that the level of hot coke within the prechamber 4 reaches the highest level when the discharge of hot coke from the coke oven and the charging of hot coke into the prechamber 4 are finished.
Therefore, the delivery rate of coke through the discharge device 8 is adjusted so that the level within the prechamber 4 reaches a minimum level when the next discharge of hot coke from the coke oven is started. In addition, combustible components combined with the circulating gas may be combusted by introducing oxygen gas into the flue 9 so that fluctuation in the amount of recovered steam is minimized while fluctuation in the discharge rate of cooled coke is minimized.
However, when the prechamber 4 is large enough to treat all the coke which is discharged from an entire coke oven battery at one time, the discharge rate of cooled coke cannot be adjusted to be the same each time.
Namely, in the case of a large-scale prechamber 4, during the period when discharging from the coke oven is being carried out the delivery rate of cooled coke through the discharge device 8 is increased, and during the period when charging of hot coke into the prechamber 4 is being stopped the delivery rate of cooled coke through the discharge device 8 is decreased. It is inevitable that the amount of steam recovered varies depending on whether the hot coke is being discharged from the coke oven or not.
When hot coke cannot be discharged from the coke oven due to a problem such as the breakdown of a pusher, the metering of coke through the discharge device 8 is adjusted depending on the level of coke within the prechamber 4.
In the worst case, as shown in FIG. 3, in which a problem occurs during discharging of hot coke from Battery A into a coke dry quencher, the discharging is stopped and the level of coke within the prechamber 4 falls below the lower limit. In that case, the removal of coke as well as circulation of the cooling gas are also stopped, and as a result, the recovery of steam is stopped.
In contrast, when the removal of cooled coke is stopped due to a problem in the discharge device 8, such as a belt-conveyor, or the like, charging of hot coke into the prechamber 4 is continued while the level within the prechamber 4 is observed. It is necessary that charging be stopped temporarily when the level in the prechamber 4 reaches the upper limit, that coke quenching be continued by switching to water-quenching, i.e., wet quenching, or that the hot coke be charged into another dry quenching apparatus for hot coke.
The problems of controlling the operation of a dry quenching apparatus become serious especially when an arrangement of batteries of coke ovens and dry quenching apparatuses like that shown in FIG. 1 is employed.
Recently, a method has been proposed to eliminate such problems. According to this new method it is possible to operate a coke dry quenching apparatus in a stable manner on a real time basis so as to optimize the operating conditions. The method comprises pre-calculating the amount of sensible heat of hot coke when discharged from an oven and the amount of combustible components of the gas on the basis of data on dry carbonization conditions and the amount and composition of starting coal, calculating the material balance and the heat balance of the dry quenching apparatus to form optimum operational data, and controlling the discharging of coke and the operation of the quenching apparatus on the basis of the optimum operational data. See Japanese Unexamined Patent Application Publication No. 63-308091/1988. However, in this method, a difference between the calculated data and the characteristics of the hot coke actually charged into the quenching apparatus is inevitable, mainly because the precalculation is carried out using data on dry carbonization and starting coal.